Abstract
Evidence showed that the developmental changes of the size of the visual span (the number of letters that can be recognized at one glance) and crowding (the inability to recognize objects in clutter) are linked to the developmental changes in reading speed (Kwon et al. 2007). However, little is known about age-related changes in the visual span and crowding and their relationships with age-related changes in reading speed. To address these questions, the visual span, crowding, and reading speed were measured in both young (mean age 24.2±3.6, n=10) and older adults (mean age 57.9±7.7, n=10) with normal vision. Visual-span profiles were measured by asking subjects to recognize letters in trigrams (strings of random three letters) flashed briefly at varying letter positions left and right of the fixation point. The size of the visual span was defined as the area under the profile, a plot of recognition accuracy as a function of letter position. Crowding was measured by asking subjects to recognize a target letter presented with flankers, at four eccentricities. Crowding zone was defined as the distance between the target and flankers required to yield 79.4% accuracy. Reading speed was measured with short blocks of text. Older adults showed significantly slower reading speed (by 25%, p=0.02) than young adults. While no noticeable decrease was found in single-letter recognition (p=0.60), older adults exhibited considerable impairment in crowded-letter recognition: significantly smaller visual span (by 18%, p< 0.01) and larger crowding zone (by 37%, p< 0.01). Both visual span (r=0.55, p=0.01) and crowding zone (r=-0.57, p< 0.01) were correlated with reading speed. Our results showed that, even in the early stage of aging, there were significant changes in the visual span and crowding. Our findings suggest that age-related decline in the ability to recognize targets in clutter may in part explain slower reading in older adults.
Meeting abstract presented at VSS 2016